Electron microscopic observations on monoamine‐containing brain stem neurons in normal and drug‐treated rats

Brain stem nuclei whose neurons contain monoamines have been surveyed by Dahlström and Fuxe ('64), using a fluorescence histochemical method. There was a diffuse fluorescence of the perikarya in these regions, with increases in catechol amine and 5‐hydroxytryptamine fluorescence after administration of dihydroxyphenylanine and pargyline, respectively. The perikarya of the locus coeruleus, nucleus dorsalis raphes and the region lateral to the nucleus interpeduncularis where numerous monoamine‐containing neurons are located, have been examined by electronmicroscopy and found not to be distinctive, except for small numbers of granular vesicles scattered in the cytoplasm. When three normal rats were compared with three given pargyline, no significant increase in the number of granular vesicles occurred in the nucleus dorsalis raphes. Thus the small number of granular vesicles does not seem to correlate with the diffuse fluorescence of these perikarya, nor does the small change in the number of granular vesicles seem to correlate with the profound increase in fluorescence after pargyline administration. It is therefore concluded that the monoamine contained in these perikarya is not located exclusively, if at all, in vesicles either of the granular or nongranular type.